Self-Assembly of Supramolecular Double Helix from a Tetrapeptide and Direct Visualization by Scanning Tunneling...

Area of Science:

• Supramolecular chemistry
• Peptide self-assembly
• X-ray crystallography and Scanning Tunneling Microscopy

Background:

• Short peptides rarely form complex superstructures like double helices.
• Understanding the driving forces behind peptide self-assembly is crucial for designing novel biomaterials.

Purpose of the Study:

• To investigate the formation and structural characteristics of a rare double-helical peptide superstructure.
• To determine whether the observed structure is an intrinsic property or an artifact of crystal packing.
• To elucidate the role of intermolecular interactions in stabilizing the peptide superstructure.

Main Methods:

• Single-crystal X-ray diffraction (XRD) to determine crystal structure.
• Scanning Tunneling Microscopy (STM) to visualize peptide assemblies at the nanoscale.
• Quantum mechanics calculations (DFT) to quantify intermolecular interactions.

Main Results:

• The peptide Z-(Aib)2-L-Dap(Boc)-Aib-NHiPr forms a stable double-helical superstructure.
• XRD and STM confirmed the double helix is an intrinsic property, not due to crystal packing.
• Intermolecular hydrogen bonds and C-H⋯π interactions were identified as key stabilizing forces, with C-H⋯π interactions contributing approximately 50% to binding energy.

Conclusions:

• The studied peptide exhibits a rare intrinsic double-helical superstructure.
• C-H⋯π interactions play a critical role in stabilizing the supramolecular double helix.
• This finding advances the understanding of peptide self-assembly and non-covalent interactions in molecular design.